Neuromuscular Junction (NMJ)

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• Neuromuscular Junction (NMJ)
• - point where the axon terminal of a nerve cell
  connects with a muscle cell.
• (gap junction)

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Synaptic cleft
NMJ at Rest
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An Action Potential (AP) reaches the synaptic end
bulb. Stimulates Ca to enter into the synaptic
end bulb. Causes the Synaptic vessicles (holding
ACh) to move to the synaptic cleft. Synaptic
vessicles release Ach into synaptic cleft
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Ach (neurotransmitter) binds to receptors on the
motor end plate. Na channels open, and Na
rushes into muscle cell. (this is the muscle
action potential)
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AT Rest
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• Na causes SR (sarcoplasmic reticulum) to release
  Ca into the sarcoplasm.
• Ca binds to T/T (troponin/tropomyosin) freeing
  actin

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• ATP on myosin head loses a P (phosphate) becoming
  ADP
• Myosin head then attaches to actin

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• Myosin head will swivel and pull the actin
  towards the m-line Power Stroke I. During
  this, the ADP falls off the myosin head.

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• A new ATP attaches to the myosin head causing it
  to release actin
• Myosin head will swivel back to its original
  position

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• ATP on myosin head loses a P (phosphate) becoming
  ADP
• Myosin head then attaches to actin

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• Myosin head will swivel and pull the actin
  towards the m-line Power Stroke II. During
  this, the ADP falls off the myosin head.

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• A new ATP attaches to the myosin head causing it
  to release actin
• Myosin head will swivel back to its original
  position

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• When the Nerve Impulse (Action Potential) stops,
  the SR will take up the Ca out of the
  sarcoplasm.
• Without Ca, the T/T complex will block actin.
• The myosin head cant attach because ATP is on
  the head and the T/T is blocked
• Elastic fibers pull actin back to its original
  position